Hi

I have removed your email address from your question for your privacy and security as this is an open forum.

I am sorry, but the only version that we make available is the version available from the App store.

If you have had Firefox installed on your Apple account before then the old version that still supported the old iOS 12.5.6 may be possible to install from your purchase history list.

Otherwise you cannot download a older version and side load install it like you may be able to do on say Android with apk.